Embattled White House national security adviser Michael Flynn resigned Monday night, an abrupt end to a brief tenure.

His departure came just after reports surfaced that the Justice Department warned the Trump administration last month that Flynn misled administration officials regarding his communications with the Russian ambassador to the United States and was potentially vulnerable to blackmail by the Russians.

“I inadvertently briefed the Vice President-elect and others with incomplete information regarding my phone calls with the Russian ambassador. I have sincerely apologized to the President and the Vice President, and they have accepted my apology,” Flynn wrote, according to a copy of his resignation letter obtained by CNN.